The present invention relates to an apparatus for displaying a travel position, which is capable of indicating the current position of a moving body on a road map presented on a screen.
Recently, in an attempt to guide a moving body, e.g. an automobile, an apparatus for displaying the current position of a moving body has been developed, in which the current position of the automobile is sequentially estimated in terms of X- and Y-coordinates by carrying out algorithmic operations on the automobile's running distance and travel direction, determined by an associated distance meter and direction sensor respectively, and the current position thus estimated is indicated in the form of a dot on a road map appearing on a screen.
However, such apparatus cannot be free from cumulation of errors in determining the running distance and direction of the automobile, which will result in an incorrect indication of the automobile's current position. For instance, an incorrect current position will cause the display dot to depart from all roads on the driver's screen, so that the driver cannot determine the road on which his car is running. In this case deformation of the road map may also occur, resulting in disappearance of the display dot from the roads indicated on the screen.
Past attempts to solve this problem have proposed that a travel trace formed by sequentially renewed estimated current car positions thereon is compared with all road patterns on the screen to find a road having the most similar pattern and then the dot image of the last estimated current car position is corrected by putting it on the corresponding position on the selected road indicated on the screen.
However, the problem still remains that if the above-mentioned matching process is applied to all the roads with no consideration for their classification, e.g. mountain road, superhighway and other ordinary roads, it may have a decreased matching accuracy depending on the class of the road whereon the car runs.
For example, any mountain road is usually characterized by large undulations and a large number of curved portions. These are represented on road maps with less accuracy than that of a superhighway or other ordinary road and, furthermore, since the data on the map are digitized by linear approximation methods to be stored in a memory such as a CD-ROM type for road map information, the stored data may include an increased amount of errors in defining a road's meandering portion having a series of sharply turning courses.
Consequently, when a car is travelling along a mountain road, it is much more difficult to make the car travel trace match the road patterns obtained on the basis of digitally processed data and displayed on the screen.